Combustion exhaust is a regulated emission. Particulate matter (PM), is the particulate component of exhaust, which includes soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, PMs can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometer range of 100 nanometers. Various technologies have been developed for identifying and filtering out exhaust PMs before the exhaust is released to the atmosphere.
As an example, soot sensors, also known as PM sensors, may be used in vehicles having internal combustion engines. A PM sensor may be located upstream and/or downstream of a particulate filter (PF), and may be used to sense PM loading on the filter and diagnose operation of the PF. The PM sensor may sense a particulate matter or soot load based on a correlation between a measured change in electrical conductivity (or resistivity) between a pair of electrodes placed on a substrate surface of the sensor with the amount of PM deposited between the measuring electrodes. Specifically, the measured conductivity may provide a measure of soot accumulation. As such, the sensitivity of the PM sensors to measure PM in the exhaust may depend on the exhaust flow rate, with increased exhaust flow rate leading to increased PM sensor sensitivity and decreased exhaust flow rate resulting in decreased PM sensor sensitivity. With this increased dependence on exhaust flow rate, the PM sensor capturing the PMs exiting the PF, may not truly reflect the PF filtering capabilities. Furthermore, PM sensors may be prone to contamination from impingement of water droplets and/or larger particulates present in the exhaust gases, thus affecting the PM sensor sensitivity and leading to errors in the output of the PM sensor.
One example PM sensor design is shown by Nelson in U.S. Pat. No. 8,225,648B2. Therein, a PM sensor includes a flow redirector and a barrier positioned around a PM sensor element to filter out the larger particulates from impinging the PM sensor element. The barrier thus serves to block larger particulates in the exhaust flow from impinging on the PM sensor element, thereby reducing PM sensor sensitivity fluctuations due to large particulates depositing on the PM sensor element.
In one example, the issues described above may be addressed by a method for flowing exhaust gas proximal to a central axis of an exhaust passage through a first opening of a cone-shaped soot sensor; expelling a first portion of the exhaust gas through a second opening directly across the first opening, and diverting a second portion of the exhaust gas around flow diverters spaced about electrodes distal to the central axis. In this way, the second opening may expel larger particulates to increase an accuracy of the sensor.
As one example, the flow diverters may further prevent larger particulates from accumulating onto the substrate. The flow diverters may be strategically spaced away from one or more surfaces of the soot sensor, based on constituents produced, such that larger particulates may entropically oppose flowing passed the flow diverters to the substrate. Additionally, by arranging the first opening along the central axis of the exhaust passage, the soot sensor may receive sufficient exhaust gas flow during a plurality of engine operating conditions. By doing this, low exhaust gas flow and larger particulate impingement may be at least partially avoided.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.